Characteristics of flow field induced by a swimming calanoid copepod*

Calanoid copepods are capable of switching swimming modes between feeding, cruising and intermittent jumping for different purposes in different environments. In this work, we report an experimental study of the flow fields induced by individual copepod (Pseudodiaptomus annandalei) swimming in a water layer without background flow, with the aid of a high-speed camera and particle image velocimetry technology. It is found that the characteristic length scales of the vortices induced by the cruising and jumping processes are 2.0±0.6 mm and 2.7±0.6 mm, respectively. However, the typical time scales for the vortex production (∼0.015s) and dissipation (∼0.15s) do not depend on the swimming behavior. The energy dissipation rate for these copepod-induced vortices is on the order of 10^-5 m²/s³. Interestingly, the flow fields induced by the feeding and jumping behaviors exhibit a -5/3 like scaling in their energy spectra, which is often reported in the inertial subrange of turbulent flows. The implications of the present results (based on individual level) for the movement pattern of population-level and in a turbulent environment will be discussed.